Rammed earth buildings are durable, strong, and visually attractive and have excellent acoustic properties. Constructing rammed earth structures involves pounding or ramming successive layers of a stabilized earth mixture into a cavity formed by a removable formwork.
However, the formwork systems presently in use can be awkward and bulky to handle, making the construction of a building a slow, labour-intensive process. It is desirable that the formwork be lightweight and easy to assemble, to disassemble and to maneuver, so that each section of the wall may be completed as quickly as possible, subject to the time taken for the ramming process.
Due to the intense forces created during the ramming process, it is also necessary that the formwork be as strong and stable as possible while still minimizing weight. To minimize the number of pieces necessary on each building site, it is preferable that each piece of the formwork be adaptable, and useful for more than one purpose, such as building several different corner shapes. In addition, it is preferable that the builders be able to access various portions of the formwork, such as the top of the cavity, to ensure the earth is being properly packed, particularly once the wall has risen above eye level.
Australian Patent No. 545,322 (the “'322 patent”) discloses a pair of spaced side panels, one solid and one portioned into sections. The panels are assembled edge to edge and are secured by suitable connecting means, which comprise tie members or a tightenable bolt assembly across the cavity between the side panels. The side panels may be supported by external brace members and, in one embodiment, by external walers mounted on the side panels or on brackets fitted on the outer side of the panels. The walers may be tightened with a bolt assembly. In use, a back side panel is assembled between two U-shaped end stops, opposed to a lower front side panel. Earth is added and rammed until the level of the earth is just below the height of the front side panel. Another front panel is set on top of the first, and earth is again packed into the cavity. The process continues until the wall is the desired height. However, the end stops of the '322 patent are simply shaped solid columns and do not appear to be adjustable. Nor do they appear to perform any other function, such as supporting the walers or providing handholds for climbing.
Regarding the strength of the formwork, the '322 patent discloses one embodiment in which there are supporting members across the cavity between the side panels, but those members are external to the cavity (i.e. outside the end stops), in order to avoid leaving through-holes in the rammed earth wall. Through-holes are generally to be avoided, since they must be plugged once the wall is complete, and because internal through-rods make it difficult to accurately position insulation within the formwork cavity. However, the external side supports disclosed in the '322 patent may pose difficulties when two connecting wall sections are being constructed. The external supports may also make it difficult to create a chamfer at an end of a wall segment, resulting in less light penetration into the structure created by the thick earth wall. Further, the '322 patent discloses a working platform associated with the side panels, and illustrates it as being quite far above the ground (see FIG. 3), but does not indicate any handholds or other means to reach the platform, on the side panels or anywhere else on the formwork.
Australian Patent No. 561,883 and Canadian Patent Application No. 2,012,959 each disclose a formwork and method for forming a rammed earth wall that is similar to the '322 patent. These patents disclose a different, more complex form of side panel, and various methods to form curves, corners and junctions in the walls. Again, neither of these patents discloses more than a simple, solid, non-adjustable end stop. In particular, Canadian Patent Application No. 2,012,959 discloses waler support shelves mounted on the side panels, but not on the end stops. The Canadian application also discloses an A-shaped external bracing structure with an adjustable means which is intended to both prop up and level the wall.
U.S. Pat. No. 2,400,852 discloses a formwork for rammed earth walls comprising side panels and pivoting posts. The main function of the invention appears to be formwork which can easily be collapsed for transport. However, the side panels and a shelf to hold a spirit level, which comprises integral leveling means, in addition to the overhead beams, are still bulky and may be awkward to transport.
While rammed earth walls tend to be very heavy and strong, internal support structures such as vertical posts may also be used to reinforce and support the wall. U.S. Pat. No. 6,718,722 (the “'722 patent”) discloses a method of wall formation which involves spraying an adobe or similar composition on an internal support structure. The '722 patent discloses a cavity, defined by a pair of walls created when frame sheets are erected outside a pair of opposed rows of posts, which may be driven into the ground or set in concrete. The cavity is filled with insulating material.
U.S. Pat. No. 6,263,628 also describes a formwork system including the need for posts in holes in the foundation. However, neither this nor the '722 patent refers to any type of apparatus for simplifying the drilling of uniformly spaced holes in the footing of a wall. The '722 patent refers to “driving” posts into the underlying soil, such as in the embodiment in FIG. 6, which is described at col. 6, line 58. The '628 patent refers to drilling a hole in the foundation on each side of a panel.
U.S. Pat. Nos. 4,768,324 and 4,702,053 describe a wall system comprising upwardly extending pins in the foundation, which are eventually encased in concrete (of which the wall is formed) to securely position the wall on the foundation. According to FIG. 4 of each patent, pins 72 appear regularly spaced in the foundation. However, no detail is provided as to how the pins are inserted into the foundation.
Rammed earth structures have a high thermal mass, so they absorb and moderate heat. However, the corollary to this is that rammed earth structures have poor thermal insulating qualities, as the walls will release the stored heat as the ambient temperature drops. For this reason, it is preferable to add a layer of insulation to each wall to stop the heat from easily passing through. While insulation may be added through linings applied to the wall's exterior surfaces, it is preferable to have the insulation within the thickness of each wall. This allows the building to reap the benefits of the insulation while retaining the appearance, low maintenance, acoustic properties and other benefits of the massive rammed earth walls.
New Zealand Patent No. 236,182 discloses a formwork and method for producing a rammed earth wall including an insulation cavity, which may be filled with air, expanded foam polystyrene or any other solid insulation material. The method of producing the cavity, such that it may be filled with insulating material after ramming, is relatively complicated.
U.S. Pat. Nos. 4,768,324 and 4,702,053 disclose formwork to create insulated concrete walls. Pairs of horizontal ladders locked into position with lock pins hold the insulated core in an upright position. Overall, the structure seems complex and difficult to construct, with several sets of ladders and bars that must be interlocked.
It can therefore be seen that one disadvantage of prior art formwork systems is that the systems are overall very bulky and difficult to transport. The end stops and sidewalls of these systems tend to be of limited adaptability. Several different pieces would therefore be required to create different wall shapes and configurations and each piece must be transported out to the construction site.
While lightweight formwork systems are preferable, it is also necessary to provide enough lateral support to the formwork to prevent bulges in the earth walls. While connectors through the bulk of the wall are well-known, such through connectors may leave unsightly holes in the wall once the formwork is removed. These holes must then be plugged individually, which is time consuming and difficult to accomplish without interfering with the thermal envelope of the wall.
In addition, the prior art formwork systems generally include end stops which are solid pieces, inserted between the sidewalls. The systems are therefore launched off their sidewalls, again limiting the adaptability of the basic formwork, requiring the use of variant pieces to create different wall shapes and curvatures. This increases the number of formwork pieces necessary to create various wall shapes.
Further, the prior art generally requires additional support structures to allow the builder to access various portions of the wall during construction.
Finally, when internal support structures (such as posts in the bed beneath the wall) are used, it can be difficult to properly space and position such structures. Such spacing is preferable, in order to provide uniform support to the wall and minimize stresses. It is therefore preferable to provide a means to quickly and accurately position internal structures, to provide the proper support without slowing down the construction process.
It is therefore an object of the present invention to provide an improved formwork system that overcomes the foregoing deficiencies. In particular, it is an object of the invention to provide a formwork system with one or more of the following features:                (a) accommodates and secures a central plane of insulation in a rammed earth wall;        (b) has no through ties to hold the side panels together;        (c) is launched off its end panels, with side panels between end panels;        (d) has integral handholds for climbing;        (e) is easily adjustable for different wall thicknesses and lengths;        (f) enables varying radii of walls;        (g) creates a soft-cornered but hefty visual appeal;        (h) is stackable, to create walls of indefinite height;        (i) has sectional end panels connected with a hinge type assembly, which are easily modified to create a 90° corner, a 45° corner and a column;        (j) contains an integral plumb bob;        (k) creates lintel-ready walls, if desired; and        (l) creates integral window and door bucks, if desired.        
Other objects of the present invention will be appreciated by reference to the detailed description of the invention that follows.